232 research outputs found
Vocational interest development from adolescence to adulthood: a meta-analysis on mean-level change
No full textInterests are among the most widely applied individual difference constructs in education and psychology. Despite their widespread usage, it is not known whether vocational interests undergo mean-level changes with age. If interests do change, in what direction? And do changes vary across age, kinds of interests, and gender? In the current meta-analysis, we aggregate effect sizes from 53 longitudinal studies on mean-level change in vocational interests, containing 98 total samples and 20,927 participants. Meta-analytic regression models were used to assess patterns of change during different age periods spanning early adolescence to middle adulthood. Results showed that mean-level interest scores increase slightly with age (d = .04). This age effect primarily involved interest in People orientation (d = .09) rather than Things orientation (d = .00). Patterns of change also varied across age categories. Mean-level interest scores decreased during early adolescence (d = -.10) before increasing throughout late adolescence (d = .09). During young adulthood, mean-level interest scores continued to change, but the direction of change varied across kinds of interests. Gender differences associated with occupational stereotypes showed distinct patterns of change across age categories. Gender gaps in Realistic and Social interests widened during early adolescence, but tended to decrease throughout the remainder of adolescence and young adulthood. Overall, findings suggest that vocational interest intensity undergoes meaningful changes from adolescence to adulthood, with theoretical and practical implications concerning the development of vocational interests.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2018-08-01The student, Kevin Hoff, accepted the attached license on 2016-07-21 at 15:22.The student, Kevin Hoff, submitted this Thesis for approval on 2016-07-21 at 15:26.This Thesis was approved for publication on 2016-07-22 at 13:43.DSpace SAF Submission Ingestion Package generated from Vireo submission #10060 on 2016-11-10 at 12:27:38Made available in DSpace on 2016-11-10T18:35:35Z (GMT). No. of bitstreams: 2
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Understanding Functional Tuning, Robustness, and Evolvability in Proteins By High-Throughput Biophysics
No full textThe history of African American women at the University of Illinois, 1901-1939
No full textThe period known as the “nadir” of the African American experience—roughly between 1880 and 1920—happens to coincide with the matriculation of the first African American students at the predominantly white University of Illinois at Urbana-Champaign (U of I). Most research conducted on the African American student experience at the U of I focuses on the Civil Rights-Black Power years, but few studies have examined the experiences of the earliest students—specifically African American women students—during the early twentieth century. These women created and sustained their own organizations—Alpha Kappa Alpha Sorority, Inc., Gamma Chapter, and later, Delta Sigma Theta Sorority, Inc., Alpha Nu Chapter—to address the educational, social, and cultural needs of African American women students on campus. In conjunction with African American male students, they established a Negro Intelligentsia lecture series, along with an African American student magazine, The College Dreamer, to promote African American culture on campus and to showcase the intellectual achievements of African American students across the country. In addition, African American women students participated on the Interracial Commission of the Young Women’s Christian Association (YWCA) to educate the campus and Urbana-Champaign community on issues concerning race and to improve race relations on campus.
This dissertation explores the multifaceted ways in which the earliest African American women students cultivated a collective consciousness while laying the foundation for their sense of agency, leadership development, and subsequent campus/community involvement. It also examines how the Gamma Chapter of Alpha Kappa Alpha Sorority, Inc. served as a conduit through which the University, as well as the chapter members, recruited more African American women to attend the U of I. Moreover, this dissertation investigates the historical experiences of African American women, the obstacles they encountered, and the manner in which they confronted those obstacles in pursuing higher education at the U of I. It provides a framework for understanding the subsequent activism of African American students at the U of I during the Civil Rights-Black Power years.Submission published under a 24 month embargo labeled 'U of I only', the embargo will last until 2017-08-01The student, Tamara Hoff, accepted the attached license on 2015-07-03 at 12:04.The student, Tamara Hoff, submitted this Dissertation for approval on 2015-07-03 at 12:21.This Dissertation was approved for publication on 2015-07-06 at 14:21.DSpace SAF Submission Ingestion Package generated from Vireo submission #8339 on 2015-09-29 at 14:59:09Made available in DSpace on 2015-09-29T20:49:42Z (GMT). No. of bitstreams: 2
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Structure-function relationships in the photoactive yellow protein family of photoreceptors
No full textThe amino acid sequence of a protein determines its three-dimensional structure, which in turn determines its functional properties. An intensively studied but still partially unresolved question is how the structure of a protein relates to its functional properties. Here we use photoactive yellow protein (PYP) as a model system to examine questions on protein structure-function relationships. PYP is a bacterial blue light photoreceptor, a prototype of the diverse PAS domain superfamily, and a model system for functional protein dynamics. The work in this thesis was directed at three aims: (1) developing tools to identify the structural change that triggers intramolecular proton transfer during the PYP photocycle; (2) the functional role of PAS-conserved residue Ile39 in PYP; and (3) determining to what extent the extensively studied structure-function relations in the PYP from Halorhodospira halophila apply to the PYP from Rhodospirillum centenum. (1) The molecular events that cause directional proton transfer in proteins are largely unknown. We develop tools to allow the testing of the specific hypothesis that the disruption of the Tyr42-pCA hydrogen bond during the PYP photocycle causes proton transfer. We developed an effective approach for obtaining Tyr-D4-labeled PYP that can be used in infrared studies to identify Tyr side chain signals. (2) The PAS domain superfamily is defined by weak but characteristic amino acid sequence conservation, but the functional role of PAS-conserved residues remains poorly understood. We examined PAS-conserved residue Ile39 through biophysical characterization of the I39A PYP mutant. This work revealed that Ile39 is at the core of a set of hydrophobic interactions conserved in PAS domains, is not an essential part in the transmission mechanism of allosteric structural changes during PYP signaling and affects both signaling kinetics and folding cooperativity. (3) We found that structure-function rules for Hhal PYP qualitatively transfer to Rcen PYP, including the role of Glu46 as the electrostatic epicenter for driving conformational changes. The resulting set of Rcen PYP mutants with altered photocycle rate and reduced conformational changes provides a powerful tool for future studies on the photocycle events that are needed for in vivo signaling by PYP
Photoreceptors Take Charge. Emerging Principles for Light Sensing
No full textKottke T, Xie A, Larsen DS, Hoff WD. Photoreceptors Take Charge. Emerging Principles for Light Sensing. Annual Review of Biophysics. 2018;47(1):291-313.The first stage in biological signaling is based on changes in the functional state of a receptor protein triggered by interaction of the receptor with its ligand(s). The light-triggered nature of photoreceptors allows studies on the mechanism of such changes in receptor proteins using a wide range of biophysical methods and with superb time resolution. Here, we critically evaluate current understanding of proton and electron transfer in photosensory proteins and their involvement both in primary photochemistry and subsequent processes that lead to the formation of the signaling state. An insight emerging from multiple families of photoreceptors is that ultrafast primary photochemistry is followed by slower proton transfer steps that contribute to triggering large protein conformational changes during signaling state formation. We discuss themes and principles for light sensing shared by the six photoreceptor families: rhodopsins, phytochromes, photoactive yellow proteins, light-oxygen-voltage proteins, blue-light sensors using flavin, and cryptochromes
Proton transfer reactions in photosynthetic water oxidation: Second sphere ligands of the manganese cluster modulate the water oxidation mechanism of Photosystem II
No full textScope and Method of Study: Physiological and Biophysical characterization of point mutations in the D1 subunit of PSII.Findings and Conclusions: In the D1-D61N mutant, it was possible to resolve a clear lag phase prior to the appearance of O2, indicating formation of an intermediate before onset of O2 formation. The lag phase and the photochemical miss factor were more sensitive to isotope substitution in the mutant indicating that proton efflux in the mutant proceeds via an alternative pathway. The results are discussed in comparison with earlier results obtained from the substitution of CP43-Arg357 with lysine and in regards to hypotheses concerning the nature of the final steps in photosynthetic water oxidation. These considerations lead to the conclusion that proton expulsion during the initial phase of the S3-S0 transition starts with the deprotonation of primary catalytic base, probably CP43-Arg357, followed by efficient proton egress involving the carboxyl group of D1-D61 in a process that constitutes the lag phase immediately prior to O2 formation chemistry. The asparagine, phenylalanine and threonine substitutions to D1-V185 were able to accumulate significant levels of charge separating PSII. Of the three substitutions the phenylalanine substitution was the most severe with a complete inability to evolve oxygen, despite being able to accumulate Photosystem II and to undergo stable charge separations. The threonine substitution had no apparent effect on oxygen evolution other than a 40% reduction in the steady state rate of O2 production compared to type Synechocystis, which can be attributed to that mutants reduced ability to accumulate PSII. The asparagine substitution produced the most complex phenotype. While still able to evolve oxygen, it does so less efficiently than wild type PSII, with a miss factor 4% higher than wild type Synechocystis. The substitution on D1-Val185 with asparagine also decreased the t1/2 of O2 release from thylakoid membranes from 1.2 ms to 10.0 ms and decreased the t1/2 lag phase prior to the onset of O2 release to 2.8 ms. The combination of a long lag period and a decreased rate of O2 release can also be observed in the D1-D61N mutant strains of Synechocystis and in PSII centers in which chloride has been replaced by iodide
Biochemical, physiological and structural characterization of AzoC, a novel azoreductase from Clostridium perfringens
No full textAzo dyes are used throughout the paper, textile, food, beverage, pharmaceutical and cosmetic industries as artificial colorants and are characterized by the presence of an azo (double nitrogen) bond. Azoreductases are bacterially-produced enzymes which are capable of breaking these azo bonds and, in some cases, can result in the production of carcinogenic metabolites. Clostridium perfringens, a common inhabitant of both the human gut and the environment, is a bacteria that produces a significant amount of azoreductase activity. The gene that encodes for this azoreductase was characterized and given the name AzoC. AzoC is very novel, as compared to similarly functioning enzymes. AzoC has been shown to preferentially reduce large molecular weight sulfonated azo dyes, such as Direct Blue 15 (992.8 g/mol), with use of NADH and FAD as cofactors. The azoreduction is much increased under anaerobic conditions as compared to aerobic conditions (4-fold greater activity under anaerobic conditions). Interestingly, with certain azo dye and cofactor conditions, the presence of the cofactors alone can cause azo dye reduction. However, with the use of an azoreductase-free control in place, this can non-enzymatic activity can be accounted for. In addition, the structure of AzoC was found to be trimeric in nature, with the AzoC monomers being held together by disulfide bonding. The secondary structure of AzoC is consistent with that of other azoreductases, despite having low sequence identity. When the azoC gene was disrupted (knocked out) by intron insertion, results suggested the presence of additional enzymes capable of azoreduction. In addition, azo dye metabolites produced following azo dye reduction were found to slow C. perfringens generation time. AzoC was found to be released following C. perfringens exposure to sulfonated azo dyes and negatively charged sulfonated compounds. This enzyme was also found to localize to the Gram-positive periplasmic region of the C. perfringens cells. The results of this study serve to fill an important gap in the literature, providing the first information on a strictly anaerobic azoreductase, as well as a link between environmental azo dye exposure and the physiological state of Clostridium perfringens cells
Insight into the light driven assembly of the oxygen evolving complex of photosystem II
No full textPhotosystem II (PSII) of plants, algae, and cyanobacteria utilize solar energy to catalyze one of the most important and most thermodynamically demanding reactions in nature: the oxidation of water into protons and molecular oxygen. Oxygen produced by PSII is toxic byproduct, however it is essential for respiration, the ozone layer and the extracted electrons drive the fixation of atmospheric CO2 to create biomass. The mechanism of water splitting driven by the light-induced charge separation is relatively well studied and high-resolution crystal structures are available to reveal the molecular aspects of PSII complex, however considerably less is known about how the inorganic Mn4O5Ca cluster is assembled de novo.The photosynthetic apparatus continuously experiences damage due to high light intensity and this results in the loss of photosynthetic activity. The primary photodamage occurs within main functional PSII unit, the D1 protein. To perform a highly efficient and sustained photosynthetic activity, damaged D1 protein should be replaced, with consequent reassembly of PSII. The key step in obtaining functional PSII de novo is the assembly of Mn4CaO5 core, driven by series of photo-oxidative reactions with incorporation of Mn and Ca ions into the coordination environment of PSII. The initial rate-limiting steps of the assembly of the PSII Mn4CaO5 core requires at least two quanta of light with the rate-limiting dark rearrangement step between them. A sensitive polarographic technique was used to track the assembly process under flash illumination as a function of the constituent Mn2+ and Ca2+ ions in genetically engineered membranes of the cyanobacterium Synechocystis sp. PCC6803 to elucidate the action of Ca2+ and peripheral proteins. We show that the protein scaffolding that organizes this process is allosterically modulated by the assembly protein Psb27, which together with Ca2+, stabilizes photoactivation intermediates.Photoactivation experiments with site-directed mutants D1-E189K and D1-E189R identified the role of D1-E189 in the formation the high affinity site of PSII. We have concluded that D1-E189 ligand is crucial during initial steps of photoactivation since it supports photoactivation intermediates by coordinating Ca2+ at its effectors site, which prevents the formation of inappropriately bound high-valency Mn at the oxygen evolving complex site
Cyanobacterial cyclic electron flow drives proton pumping through NDH-1 complexes
No full textIn cyanobacteria and other photosynthetic organisms, cyclic electron flow (CEF) around Photosystem I (PSI) is a crucial mechanism for balancing the photosynthetically produced energy carriers NADPH and ATP that are utilized to accumulate biomass. This is accomplished via the oxidation of NADPH by membrane oxidoreductases which pass the electrons into the membrane-soluble PQ pool and back to PSI where ferredoxin (Fd) and NADP+ are reduced, completing the cycle. This cyclic flow drives the pumping of protons across the thylakoid membrane, driving the operation of ATP-synthase and thereby increasing the ATP/NADPH ratio with no net consumption of NADPH. A major participant in CEF are the NDH-1 complexes, homologs to respiratory complex I. Cyanobacteria possess four versions of this complex that participate in CEF as well as CO2 uptake. While the activity of these complexes in pumping protons is known in other organisms, and the closely related chloroplast NDH-1 had recently been shown to do so, information on these complexes in cyanobacteria is lacking regarding proton pumping activity. As well, in cyanobacteria, these complexes were demonstrated to utilize Fd as a reductant source instead of NAD(P)H as is typical for its homologs. Cyanobacteria also possess a system to regulate the redox state of the Fd/NADPH pools by exchanging electrons between them, termed the Fd:NADP-oxidoreductase (FNR). Some cyanobacteria, like Synechocystis sp. PCC6803, possess two isoforms of FNR, FNRS and FNRL, that share a gene and are differentially expressed by different translation initiations, and are thought to primarily operate in NADPH oxidation and NADP+ reduction respectively, though there are still large gaps in understanding their physiological functions. In this work, it is hypothesized that CEF is a major driver of proton pumping and that NDH-1 complexes are the driving force of that proton pumping. It is also hypothesized that the activity of FNRS feeds NDH-1 with reduced Fd, allowing enhancement of proton pumping during acclimation to fluctuating light conditions, a major stressor of photosynthetic organisms
Structural dynamics of photoactive yellow protein
No full textPhotoactive yellow protein (PYP) is a blue light photoreceptor protein. PYP is a structural prototype of the PAS domain superfamily of regulating and signaling proteins. Upon absorption of a blue light photon, PYP exhibits a photocycle leading to the signaling state. We study structure-function relation in the PYP family by investigating single point mutants of Halorhodospira halophila (Hhal) PYP and homologous PYPs from three different bacteria. We study the role of Asn43 in Hhal PYP, a one of the nine well conserved residues in the PAS domain superfamily. The time-resolved FTIR difference spectroscopy of Asn43Ala PYP shows that this residue plays a key role in regulating kinetics of signaling of PAS domain. The FTIR absorption spectrum of Idiomarina loihiensis (Il) and Hhal PYP shows that the secondary structures of the Il PYP are similar to that of Hhal PYP. The decay of long lived putative signaling pB state of Il and Hhal PYP follows similar kinetics, yet these PYP perform different biological functions. We have observed a novel spectral isotopic effect (SIE) in Salinibacter ruber (Sr) and Hhal PYP through UV/Vis absorption spectroscopy. SIE offers possibility to examine hydrogen bonding strength in proteins.Despite extensive studies since 1887 ( Arc. Exp. Pathol. Pharmacol. 1887, 29: 1-16), it remains unclear how salt solutions alter stability and solubility of protein. We employ PYP as a model system to study impact of salts on structural dynamics of protein. The time-resolved step-scan Fourier transform infrared spectroscopy (FTIR) with 5 mus time resolution and time-resolved rapid-scan FTIR with 8 ms time resolution were employed in this study to capture the dynamic structural development of PYP upon light stimulation. We found that salts do not alter photoisomerization of p-coumaric acid (pCA) and proton transfer pathway from Glu46 to pCA upon photoexciation of PYP. Thus salt do not affect structural changes inside protein. Our study reveals that, salt suppresses conformational changes of PYP strongly, thus formation of signaling state of PYP for bacterial phototaxis is inhibited in high salt solutions. The suppression of conformational changes of PYP signaling state in high salt solution is attributed to effective dehydration of proteins. The knowledge gained may be applied to understand the effect of high salt concentration on stability and solubility of the proteins, which is known as Hofmeister effect
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